PROJECT SUMMARY/ABSTRACT Lyme disease (LD) results from infection with the spirochete Borrelia burgdorferi transmitted via the bite of a tick. It is the most common arthropod-borne disease in the United States. B. burgdorferi is maintained in a natural enzootic cycle, alternating between a vertebrate host reservoir, usually a small mammal, and an Ixodes tick. How B. burgdorferi senses and adapts to these disparate environments to complete its enzootic cycle, and thus persist to remain a public health problem, is not well understood. In this application, we propose to investigate a novel signaling pathway that regulates the interaction of B. burgdorferi with its tick vector. Our central hypothesis is that carbonyl stress, mediated by the overlooked metabolite methylglyoxal (MG), has an important role in persistence of the spirochete in the tick. MG is produced in bacteria by methylglyoxal synthase (MgsA), which converts dihydroxyacetone phosphate to MG and inorganic phosphate. Our preliminary data indicate that this activity is likely to occur in the tick, is dependent on MgsA and post-translationally glycates specific target proteins. In Aim 1, we propose to genetically and biochemically define the carbonyl stress pathway and the regulation of MG production in B. burgdorferi. We will also examine the role of the carbonyl stress pathway in the tick-mouse model of LD and identify the proteins targeted for glycation by MG. In our second aim, we propose to genetically dissect MgsA function in LD Borrelia by comparative analyses with RF Borrelia and B. mayonii to better understand the role of carbonyl stress in vivo. The long-term objective of our proposal is to understand the unique strategies and mechanisms B. burgdorferi uses to persist in the tick and transmit to mammals, which may lead to improved diagnostic, prevention, and treatment strategies; this is relevant to the mission of the agency to ?seek fundamental knowledge? for the sake of alleviating human disease.